1. Field of the Invention
The present invention relates to a radio communication system, a base station control equipment, a radio terminal, and a radio communication method which performs communication via a radio channel, and more particularly to those which can perform communication among channels or systems having a different communication speed.
2. Description of the Related Art
In recent years, radio communication system represented by mobile communication, which does not require laying down wired cables, has been used as a communication system in various environments. Among them is mobile communication system using CDMA (Code Division Multiple Access) technology. In the mobile communication system using CDMA technology, communication is performed by using a plurality of radio signals as communication channels, which are created by spreading one frequency band by a plurality of codes mathematically orthogonal to each other. In an overlapped area of the communication areas by a plurality of radio base stations, as a handover operation, a mobile station establishes path connection with each of the radio base stations of the communication area and thereby performs communication. More specifically, a mobile station transmits/receives data to and from multiple radio base stations using the same frequency and speed via a plurality of paths.
In recent years, radio communication techniques using wireless LAN have also been used. In the radio communication using the wireless LAN, a radio terminal accesses an access point arranged at a predetermined position and thereby performs radio communication. In this case, communication is performed at a communication speed different from that of the above described mobile communication system using the CDMA technology.
The two radio communication systems described above performs radio communication at a different communication speed from each other. Accordingly, when performing communication while moving, a radio terminal cannot perform seamless changeover between the two radio communication systems.
In Japanese Patent Laid-Open No. 2003-9224, there is disclosed a technique of radio communication system which has two base stations having a different communication speed from each other. In this technique, a path control equipment, which selects one of two communication networks each connected to the each base station, is provide, and performs communication between the base station and a radio terminal via the communication network selected by the path control equipment. In the radio communication system disclosed in Japanese Patent Laid-Open No. 2003-9224, control information, which indicates whether high speed data transmission from the base station can be acceptable or not to the radio terminal, is sent from the radio terminal. And, one is selected from among the two communication networks based on the control information. Accordingly, it is possible for the radio terminal to communicate with communication networks having a different communication speed each other.
In the radio communication system disclosed in Japanese Patent Laid-Open No. 2003-9224, however, the control information must be sent from the radio terminal prior to selecting one of communication networks. Consequently, under the radio signal propagation environment is not good and when the radio signal state of a high speed channel frequently deteriorates, the processing in the radio terminal may become complex.